<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
    <style>
        .flex-container {
            display: -webkit-flex;
            display: flex;
            -webkit-flex-wrap: wrap;
            flex-wrap: wrap;
            /*width: 300px;*/
            height: 250px;
            background-color: lightgrey;
            align-content:flex-start;
        }

        .flex-item {
            background-color: cornflowerblue;

            height: 200px;
        }
    </style>
</head>
<body>

<div class="flex-container">
    <div class="flex-item">flex item 1</div>
    <div class="flex-item">flex item 2</div>
    <div class="flex-item">flex item 3</div>
</div>

</body>
</html>
